1. Field of the Invention
The present invention relates generally to ultrasonic dental scalers, and more particularly relates to an oscillating circuit for vibrating a dental scaler insert tip at its ultrasonic resonant frequency.
2. Description of the Prior Art
It is known in the art to clean calculus from teeth using an ultrasonic dental scaler. Generally, in an ultrasonic dental scaler, vibrational motion of a transducer is transformed to flexural or elliptical motion of a dental scaler insert tip. Common frequencies of operation are 25 kHz and 30 kHz, although frequencies as low as 18 kHz and as high as 40 kHz have been used. The vibratory motion of the scaler insert tip is used to dislodge calculus from the teeth of a patient. In most cases, the scaler also includes a means for irrigating the area around the scaler tip by dispensing a liquid, such as water, through or over the surface of the scaler tip.
Magnetostrictive ultrasonic dental scalers usually include a dental handpiece having an ultrasonic transducer positioned within an energizing coil located within a sleeve. The transducer or scaler insert conventionally comprises a stack of laminar plates of magnetostrictive material that is excited by the energizing coil to longitudinally expand and contract the transducer at an operational resonant frequency. Conventional dental scalers are designed to operate at one specific frequency, usually 25 kHz or 30 kHz. Thus, a dentist would need to have two dental scaler devices in order to be able to use scaling inserts having different resonant frequencies. This is usually impractical due to space limitations as well as cost factors. Accordingly, the dentist is forced to choose a resonant frequency of operation and can only use scaling inserts having the chosen resonant frequency.
To properly vibrate the scaler insert, the electronic circuit generally includes an oscillating circuit having a variable output amplitude. The frequency of the oscillator is adjusted to the mechanical resonance of the scaling insert. Traditionally, this adjustment or tuning was achieved by either a manually tuned circuit adjusted by the dentist for optimum vibration or automatically using a feedback coil in the handpiece coupled to associated control circuitry to electronically adjust a variable frequency oscillator to the correct output frequency.
The feedback coil is generally formed by winding a very fine wire near the base of the handpiece. The feedback coil of fine wire is provided to register a voltage developed by the movement of the ultrasonic scaler insert within the electro-magnetic field of the handpiece. Associated control circuitry uses this information to electronically adjust the variable frequency oscillator to the correct output frequency. The feedback coil tends to be very fragile due to the fine gauge wire from which it is formed. Additionally, the feedback coil requires that an extra conductor be placed in the handpiece cable coupling the feedback coil at the base of the handpiece to the device electronics located in a separate housing. Thus, the feedback coil tends to be a common source of malfunction or failure of conventional dental scalers.
Conventional dental scalers also include a power setting to allow the dentist to adjust the power or amplitude of vibration depending upon the needs of the dentist during the cleaning procedure. During the removal of calculus, it may be necessary to increase the power to the scaler tip to break the calculus from the tooth surface. This power setting is most commonly performed by turning a power adjustment knob located on the housing containing the electronic circuit. Once the stubborn piece of calculus is removed, the power must again be adjusted to a lower setting to provide adequate cleaning power and for patient comfort. Consequently, the dentist may have to adjust the power setting several times during a cleaning procedure. The necessary adjustments are time consuming and prolong the cleaning procedure. It would therefore be advantageous to have a means for quickly adjusting the power setting of the dental scaler to suit the needs of the dentist.
Thus, the present invention is directed toward overcoming the disadvantages of conventional dental scalers which have been discussed above.